From the point of view of chemistry, activated carbon is one of the forms of carbon with an imperfect structure, practically free of impurities such as hydrogen, nitrogen, halogens, sulfur, and oxygen.
The imperfect form is characterized by a high degree of porosity with pores, the size of which varies over a wide range with limits differing by more than 106 times – from visible cracks and crevices to various gaps and voids at the molecular level. It is the high level of porosity that makes the activated carbon “activated”.
Appearance – black amorphous granules or powder, carbonized carbonaceous material of various sizes and shapes.
In its chemical composition, activated carbon is similar to graphite, the material used in conventional pencils. Activated carbon, diamond, graphite – all these are forms of carbon, practically free of impurities.
The intermolecular attraction that exists in the pores of coal leads to the emergence of adsorption forces, which by their nature are akin to the force of gravity, with the only difference that they act on a molecular rather than an astronomical level. They are called Van der Waals forces.
These forces cause a precipitation-like reaction in which adsorbents can be removed from water or gas streams.
Chemical reactions and chemical bonds can also occur between adsorbents and the surface of activated carbon or inorganic impurities. These processes are called chemical adsorption or chemisorption.
However, it is the process of physical adsorption that occurs during the interaction of activated carbon and an adsorbing substance.
The pore structure of activated carbon
In inactivated carbons, three categories of pores are distinguished: micro-, meso- and macropores. Micro- and mesopores make up the largest part of the surface of activated carbons. Accordingly, it is they who make the greatest contribution to their adsorption properties. Micropores are particularly well suited for the adsorption of small molecules and mesopores are particularly well suited for the adsorption of larger organic molecules.
The starting materials for their production have a decisive influence on the pore structure of activated carbons. Activated carbons based on coconut shells are characterized by a greater proportion of micropores, and activated carbons based on coal, by a greater proportion of mesopores. A large proportion of macropores is characteristic of wood-based activated carbons.
Molecules of the removed pollutants are retained on the surface of activated carbon by intermolecular van der Waals forces. Thus, activated carbons remove contaminants from the substances to be purified (in contrast, for example, from discoloration, when the molecules of colored impurities are not removed but are chemically converted into colorless molecules).
The effectiveness of coal as an adsorbent depends on the size of its available surface area. The adsorption efficiency can also be influenced by factors such as the size of the adsorbate molecules, the size of the pores and granules of the coal, and the temperature and pH of the solution.
The use of activated carbon
With the development of industrial production of activated carbon in the early 20th century, the use of this product is constantly growing.
Today, activated carbon is used in many processes of water purification, the food industry, in the processes of chemical technology. In addition, the treatment of gases and effluents is based mainly on adsorption by activated carbon. And with the development of nuclear technology, activated carbon is the main adsorbent of radioactive gases and effluents in nuclear power plants. In the 20th century, the use of activated charcoal appeared in complex medical processes, such as hemofiltration (purification of blood on activated carbon).
We offer coal for different applications:
Some substances are weakly adsorbed on the surface of conventional activated carbons. These substances include ammonia, sulfur dioxide, mercury vapor, hydrogen sulfide, formaldehyde, chlorine, hydrogen cyanide.
For effective removal of such substances, activated carbons impregnated with special chemical reagents are used.
Currently, activated carbon is mainly produced in the following 4 forms.
Forms of activated carbon
granular activated carbon;
powdered activated carbon;
extruded activated carbon (extruder);
activated carbon impregnated fabric.